There has been a growing interest in the use of metallocenes for polyolefin production. Many metallocenes for polyolefin production are difficult and time-consuming to prepare, require large amounts of alumoxane, and exhibit poor reactivity toward higher olefins, especially for making ethylene-alpha olefin copolymers and ethylene-alpha olefin-diene terpolymers. Moreover, the ethylene-alpha olefin copolymers and ethylene-alpha olefin-diene terpolymers prepared using these metallocenes often have undesirably low molecular weights (i.e., Mw less that 50,000).
The so-called "constrained geometry" catalysts such as those disclosed in EP 0 420 436 and EP 0 416 815 can provide a high comonomer response and a high molecular weight copolymer, but are difficult to prepare and purify, and, therefore, are expensive. Another drawback of the bridged amido-cyclopentadienyl titanium catalyst system is that in order to form an active oxide-supported catalyst, it is necessary to use fairly high levels of alumoxane (see, e.g., WO96/16092) or to employ mixtures of aluminum alkyl and an activator based on derivatives of tris(pentafluorophenyl)borane (see, e.g., WO95/07942), itself an expensive reagent, thus raising the cost of running the catalyst. In the constrained geometry catalyst art, such as in EP 0 416 815 A2 (page 2, lines 5-9 and 43-51), it is pointed out that the angle formed by the cyclopentadienyl centroid, transition metal, and amide nitrogen is critical to catalyst performance. Indeed, comparison of the published result using a bridged amido-cyclopentadienyl titanium systems with similar unbridged systems has generally shown the unbridged analogs to be relatively inactive. One such system, described in U.S. Pat. No. 5,625,016 shows very low activity, while having some of the desirable copolymerization behavior.
In contrast to the constrained geometry catalysts, the catalyst of the invention is unconstrained or unbridged and relatively easily and inexpensively prepared using commercially available starting materials. Further, the level of aluminoxane utilized can be lowered. That is, in the present invention, the precursor can be dried onto a support or with a spray drying material with Al:Ti ratios below 100:1 to form highly active catalysts with similar polymerization behavior to their unsupported analogs of the invention and polymerization behavior similar to constrained catalysts.
In Idemitsu Kosan JPO 8/231622, it is reported that the active catalyst may be formed starting from (C.sub.5 Me.sub.5)Ti(OMe).sub.3 and that the polymer formed has a relatively wide or broad compositional distribution. The present invention does not utilize this precursor.
Typically, polyolefins such as EPRs and EPDMs are produced commercially using vanadium catalysts. In contrast to polyolefins produced using vanadium catalysts, those produced by the catalysts of the present invention have high molecular weight and narrower composition distribution (i.e., lower crystallinity at an equivalent alpha olefin content.
There is an on-going need to provide a catalyst employing a metallocene which is easy to prepare, does not require large amounts of aluminoxane and which readily copolymerizes to produce ethylene-alpha olefin copolymers, ethylene-alpha olefin-diene terpolymers, and polypropylene, as well as producing polyethylene.